1. Field of the Invention
The present invention is directed in general to the field of semiconductor devices. In one aspect, the present invention relates to MEMS devices and methods for fabricating MEMS devices.
2. Description of the Related Art
Micro-Electro-Mechanical Systems (MEMS) technology is increasingly used to integrate mechanical elements, sensors, actuators, and electronics on a common silicon substrate through microfabrication technology. For example, inertial sensors may be formed with MEMS devices on an integrated circuit wafer substrate to form various applications, such accelerometers for measuring linear acceleration, gyroscopes for measuring angular velocity, optical devices, pressure sensors, switches, and so forth. A conventional MEMS device typically includes a moveable element, such as a proof mass, diaphragm, mirror, and the like that is flexible or movable, and is attached to the rest of the device. Relative motion between this movable element and the rest of the device is driven by actuators and/or sensed by sensors in various ways, depending on device design. With existing semiconductor processing techniques, there are challenges with integrating multiple MEMS sensors onto a single integrated circuit device, such as when different MEMS sensors operating at different cavity pressures are separately fabricated and assembled into a single substrate layer, resulting in a combined sensor circuit having a large footprint and potentially conflicting processing steps. For example, the bonding techniques used to form a good vacuum for a first sensor (e.g., gyroscope sensor) may be unsuitable for another sensor (e.g., an overdamped accelerometer) formed on the device substrate. In addition, the getter materials used to form a vacuum in a gyroscope wafer cavity can impose additional expense as well as processing constraints for the formation of other MEMS sensors due to the temperature limitations of such getter materials. Conversely, the anti-stiction coatings used in forming accelerometer sensors can interfere with the eutectic bonding process used to form gyrometer sensors. As a result, the existing design, operation, and manufacturability of integrated circuit MEMS sensors are extremely difficult to implement at a practical level.